1. Field of the Invention
The present invention is directed to silicate based glass compositions with nitrogen compounds included in the composition as performance modifiers and the methods of making the composition and glass articles formed therefrom. More particularly, the present invention is directed toward the use of metal nitrides in silicate based glasses for the improvement of spectral properties such as the absorption of infrared energy.
2. Summary of Related Art
Performance modifiers and colorants are often added to base glass compositions to impart specific color and energy transmittance properties in the finished glass. The absorption of energy at specific wavelengths is often desirable to enable various uses for the glass compositions. Additionally, certain colors are preferred for various glasses for aesthetic reasons. There are limitations within specific glass compositions that must be balanced or optimized when attempting to achieve desired color and energy transmittance properties. For example, certain ingredients may improve the absorption of near infrared energy while imparting an undesirable color or reducing the light transmittance. Thus, the optimization of a specific color or energy transmittance property often negatively impacts other desirable transmittance properties.
The present invention utilizes metal nitrides in silicate based glass compositions to improve either color or energy transmittance properties of the finished glass. The use of a metal nitride results in the unexpected improvement of color and energy transmittance properties when added to conventional silicate based glass compositions. Different metal nitrides will impact the silicate based glass in different manners. Thus, the selection of a specific metal nitride is dependent upon the silicate based glass composition, the additional colorants in the composition, and the desired color or energy transmittance properties. For example, the inclusion of a metal nitride in a soda-lime-silica glass, containing an iron colorant, exhibits a reduction in the transmittance of near infrared energy over similar non-nitride containing compositions, without adversely affecting the visible light transmittance.
Silicate based glass batch compositions recognized within the art may include nitrogen compounds in the form of nitrates. Sodium nitrate, or niter, is generally utilized to improve the retention of the colorant selenium in the finished glass. The nitrate does not improve the spectral performance of the finished glass.
Also, infrared absorbing, or heat reducing, silicate glasses are known within the art. In general, infrared absorbing silicate glasses involve the addition of specific colorants that impact the color and energy transmittance properties of the glass.
For example, U.S. Pat. No. 4,792,536 discloses a process for producing an infrared energy absorbing glass, containing a low total iron concentration which is highly reduced to FeO. It is further disclosed that the infrared energy absorption can be increased by including greater amounts of total iron in the glass composition, but states that the visible light transmittance would thereby be reduced below levels considered adequate for automotive glazings. The patent teaches that the iron must be at least 35% reduced to FeO.
Another example of an infrared absorbing silicate glass is found in U.S. Pat. No. 5,077,133. The patent discloses a green colored infrared and ultraviolet absorbing silicate glass which includes an amount of ceric oxide, or alternatively ceric oxide and titanium dioxide, and a high concentration of moderately reduced iron. The glass composition exhibits a visible light transmittance of at least 70% and a total solar energy transmittance of less than 46%. Although the glass composition exhibits a low solar energy transmittance, it is desirable to further reduce the total solar energy transmittance, through the absorption of near infrared energy, while maintaining the high visible light transmittance.
It would be an advantage to provide a performance modifier for use in a silicate glass composition that significantly improves color and energy transmittance values without adversely impacting other transmittance properties in the finished glass.